Microbial Fungi On Grapes Can Influence The Character Of Wine

At first blush, winemaking appears to be a relatively simple process — crush grapes, extract juice and ferment. However, even the most cursory examination of the factors involved in the process opens a Pandora´s Box of important details.

That level of detail was made all the more explicit by a new report in the open access journal PLOS ONE, which said the grapes from the same vineyard can vary widely with respect to the microbial communities present on their skins.

“In the wine industry, the fungal communities on grapes are especially important. The microbial species present on the berry may contribute to the fermentation process, and therefore the aromatic properties of the resulting wine”, the authors explain.

For this study, researchers from the Institute for Wine Biotechnology at Stellenbosch University in South Africa picked Cabernet Sauvignon grapes from different vines in three commercial vineyards that each used different cultivation methods: organic, traditional and biodynamic.

The research team used the so-called Theory of Sampling (TOS) method to select their grape samples, which linearizes a two-dimensional area into a one-dimensional vector. The theoretically highly-efficient sampling is then performed along this vector.

To survey the variety of microbes present, yeasts from the grapes were counted on Petri dishes, genetically sequenced and molecularly analyzed.

The comprehensive analysis showed that several of the same yeast species dominated all three vineyards. The researchers also found that the least treated vineyard had a greater variety of fungal species than the other two. They also noted that small differences among vines, such as fluctuations temperature or sun exposure, significantly altered the make-up of the fungal community on the grape skins.

Some of the fungal species found by the researchers are easily cultivated and the researchers said that they could be grown or encouraged to create a desired effect in a particular vintage.

The authors concluded that more in-depth studies could investigate the microbial communities on a larger scale.

“[I]t would be important to evaluate the microbial diversity over several vintages and at different grape ripening stages to confirm whether the distinction between the vineyards is persistent,” they wrote.

In addition to seeing how fungal communities are distributed across a vineyard, researchers have also been looking into how climate change may be affecting grapes and the winemaking process.

New York Times contributor Paige Donner is currently working on a documentary based on her 2011 investigative report that made the connection between wine and climate change. She found that the shift to a warmer climate is likely to bring both positive and negative effects.

Warmer temperatures allow for vineyards to expand by planting more vines. However, some grapes can be affected by temperature fluctuations of just a few degrees. For example, Pinot Noir grapes lose their distinctive full-bodied character when grown outside their ideal temperature range, while the vines that produce chardonnay grapes will produce less acceptable fruits if they are grown in an environment that is either too hot or too cold by even a few degrees.